Water-soluble polymeric substances have found great utility in industry for applications such as sludge dewatering. They are used to flocculate dispersed particulate solids from aqueous suspensions, including sewage and effluents from industrial, mining and paper manufacturing operations.
Cationic and cationic quaternary ammonium polymers having excellent performance in sludge dewatering are delivered preformed or are made on-site. Neutral polymer is reacted with formaldehyde and a secondary amine or with a premix of formaldehyde and a secondary amine to form a cationic polymer and optionally followed by reaction with a quaternizing agent such as dimethylsulfate or methyl chloride to form cationic quaternary ammonium polymers. When a premix is used, it is made shortly prior to reaction with the neutral polymer.
U.S. Pat. No. 3,979,348 teaches preparing an aqueous solution of a formaldehyde/secondary amine adduct, preferably in as concentrated a form as possible so as to minimize dilution effects on the end product. It teaches that, due to the concentrations of commercial aqueous solutions of formaldehyde and of aqueous amines, the concentration of the adduct is between 0.1 to 55 weight percent (wt. %).
U.S. Pat. No. 4,010,131 teaches reacting an aldehyde and a secondary amine to make an aldehyde/amine adduct in a 0.1 to 55 wt. % aqueous solution. The adduct is reacted with the polymer in a water-in-oil emulsion system followed by quaternization of the polymer using an alkylating agent.
U.S. Pat. No. 4,230,608 also teaches the reaction of a water-soluble polymer such as polyacrylamide with a formaldehyde/secondary amine premix followed by quaternization with an alkylating agent such as dimethylsulfate or methyl chloride. In each exemplification, the premix was reacted with the polymer shortly after being made.
U.S. Pat. No. 4,390,659 teaches a method for preparing these same quaternary polymeric complexes by simultaneously contacting a water soluble polymer with a lower aldehyde such as formaldehyde and a secondary amine such as dimethylamine, or the reaction product thereof, and a quaternizing agent. "Simultaneously contacting" means that the polymer, amine, aldehyde and at least a portion of the quaternizing agent are contacted prior to the substantial reaction of the polymer with the amine, aldehyde or their reaction product.
U.S. Pat. No. 4,049,606 teaches cationically modified polymers of acrylamide prepared by adding an aqueous solution of formaldehyde followed by adding a lower alkyl secondary amine.
U.S. Pat. No. 3,539,535 teaches a process for producing water-soluble, cationic carbamoyl polymers in the form of particulate solids by reacting carbamoyl polymers with formaldehyde and water-soluble, mono-functional, secondary amines. The formaldehyde and the amine are added simultaneously or as a premix.
U.S. Pat. No. 4,179,424 teaches adding formaldehyde and secondary amine to an acrylamide polymer. Paraformaldehyde dissolved in water is taught as a substitute for the 10 to 50 wt. % aqueous formaldehyde. In the Mannich Reaction Experiment, the formaldehyde and the amine were premixed if the reactor temperature was 100.degree. C. and added in less than 15 seconds. Otherwise, the formaldehyde and the amine were simultaneously added to the polymer.
On-site preparation of formaldehyde-secondary amine adduct premix has several limitations.
For example, the amine and aldehyde must be shipped and stored by the user with the attendant added cost and risk of exposure to toxic chemicals. Both the aqueous aldehyde and the anhydrous or aqueous dimethylamine typically used in water treatment require special handling and storage considerations in that they have objectionable odor, are toxic and, in the case of the aqueous compounds, contain water that increases freight costs and the amount of storage needed. In the case of the anhydrous dimethylamine, pressure vessels are needed for shipping and storage.
A less odoriferous, more stable material that could be shipped and stored in non-pressure vessels and that could be added to a solution of the water-soluble polymer on-site to make a Mannich modified polymer that can be quaternized and is effective for dewatering sludges would be desirable.
Applicant has found that by limiting the water content of the adduct to 30 wt. % or less that an adduct of improved stability results. Also, he has found that further improvements, particularly when storage is at higher temperatures, can be achieved through the addition of a straight chain C.sub.1-3 alkyl alcohol. In the absence of added alcohol, lower temperatures improve stability. Thus, the adduct premix need not by made just prior to use. A premix can be made and shipped to the place of use. The user then needs only one storage facility for the adduct instead of one for the formaldehyde and one for the amine. Because the product contains less water, shipping, handling and storage costs are reduced.